Are we alone? The question hangs over each discovery of an Earth-sized planet as we speculate on its habitability. But how different and varied could these worlds really be? Perhaps the best way to get a flavor of this potential diversity is to build a few planets.
This is the idea behind Earth-Like: a website and twitter bot that lets you build your own Earth-like world. Earth-Like begins with a planet that resembles our Earth today, with oceans flowing over the surface and an atmosphere that maintains the global average temperature at a comfortable 15°C (59°F) on our orbit within the habitable zone. By making changes to the fraction of exposed land, the volcanic rate and position within the habitable zone, you can change the conditions on our planet into wildly different environments from desert to snowball.
The concept for Earth-Like began during a workshop on planet diversity held at the Earth-Life Sciences Institute (ELSI) in Tokyo. The discussions highlighted that the potential for variation between rocky worlds is vast. A planet rich in carbon could have a mantle of diamond. A stagnant surface rather than mobile continental plates could throttle volcanism. The gravity on a large rocky planet might flatten the topology to allow shallow seas to cover all the land.
At the moment, observations can only tell us the physical size (either radius or mass) and the orbit of the majority of extrasolar planets. As we do not know what the surface of these worlds is like, we dub new discoveries Earth-like or potentially habitable if their size and the amount of radiation they receive from the star is similar to Earth. But this fails to convey how incredibly alien these worlds could be.
Earth-Like was spearheaded by undergraduate student, Kana Ishimaru, at the University of Tokyo (now a graduate student at the University of Arizona), working with myself, Julien Foriel (now a researcher at Harvard University) and Nicholas Guttenberg at ELSI. We wanted to build a model that would give a feel of the diversity of potentially habitable worlds and which could be run easily on a web browser.… Read more